According to a prior art barring gear assembly, the turning function is executed by an electric motor driving a first gear by means of a hydraulic coupler. This initial reduction is obtained through a pinion mounted on the shaft motor and a guided wheel fixed on a secondary shaft. The secondary shaft is connected to the shaft via a second gear whereof one wheel is fixed to a clutch. The clutch disconnects the barring gear assembly from the shaft. All the components are lodged into a box, except the electric motor and the hydraulic coupler. Such an arrangement has a certain number of disadvantages:                the presence of the clutch on the shaft makes maintenance operations of the barring gear assembly highly complex. Disassembling the barring gear assembly requires disassembling of the components located between this clutch and the closest end of the shaft. This especially implies long and complex adjustment operations as each component is reassembled. In particular, the presence of the clutch on the shaft disallows positioning of the barring gear assembly between two rotors of the shaft.        the flexible coupling between the hydraulic coupler and the endless screw placed inside the box are subjected to the atmosphere caused by oil projections and oil vapour. Its shelf life is thus seriously shortened.        accessibility to the clutch is very difficult,        the arrangement is not optimal. The presence of the clutch on the shaft necessarily extends said shaft. The general bulk of the turbo-alternator group is thus increased.        